A preferably signed measurement of the motor current for a clocked application, that is to say for example an application in which the motor is operated on an H-bridge, requires a high level of circuit complexity, since both motor connections are clocked continuously, that is to say they are supplied with pulsed power, and the potential is therefore shifted with respect to evaluation electronics.
An H-bridge is in general an electronic circuit comprising four switches, and is preferably formed using transistors and/or power semiconductors. The H-bridge converts a DC voltage to an AC voltage at a variable frequency and with a variable pulse width. A circuit such as this is used in particular for driving direct-current motors and for selection of the rotation direction. However, an H-bridge can also be used to feed a transformer from DC voltage power supply systems. Furthermore, an H-bridge is used, for example, in modern switched-mode power supplies.
The clocking process results in the motor current having an alternating component whose magnitude depends on the terminal voltage, the duty ratio, or the pulse to pause ratio, of a pulse-width modulation signal and the effective inductance of the motor. The measurement of any given instantaneous value of the motor current is therefore always subject to some uncertainty relating to the alternating component. According to the prior art, in order to avoid a measurement error, for example caused by so-called current ripple, a plurality of measured values are recorded and are determined by means of an averaging process, for example by means of a low-pass filter with a cut-off frequency which corresponds to a fraction of the clock frequency. The measured value determined in this way is then available only with a corresponding time delay.